This research is directed toward understanding the two primary functions of low density lipoprotein (LDL), i.e., the transport of cholesterol and phospholipid and the transfer of these lipids to cells and extracellular tissues. These are functions which are mediated by the protein of LDL, apolipoprotein B (apoB). The primary concern of our research is towards understanding how apoB functions in these roles, and our current efforts are directed towards characterizing this apoprotein. Recently, we have reported the solubilization of apoB in denaturing solvents. Presently, we are completing a physical characterization of apoB in a variety of denaturing solvents and also investigating the influence of associated lipid on these properties. ApoB is an immunologically reactive protein and as part of its charcterization the antigenic properties of the protein are also being studied. Several years ago we described a means for preparing partially trypsinized LDL which resulted in the production of peptides from apoB which varied in size from about 10,000 to 100,000. The separation of these peptides has proven to be a tedious process; however, this remains an ongoing effort in this laboratory.